1. Field of the Invention
The present invention relates to an exposure apparatus and a device producing method using the exposure apparatus. Particularly, the present invention relates to a scanning exposure apparatus in which each portion of a mask pattern is projected on a corresponding portion of a substrate to be exposed by simultaneously moving the mask and the substrate relative to an exposure beam, and a method of producing a device such as a semiconductor memory, a magnetic head, a liquid crystal panel, a CCD or the like using the scanning exposure apparatus.
2. Description of the Related Art
FIG. 17 shows an illuminating optical system and a projection optical system in a reflection type projection exposure-apparatus in which a mask pattern image is transferred to a substrate coated with a photosensitive material by using ultraviolet light emitted from a super-high-pressure mercury lamp. In FIG. 17, the ultraviolet light emitted from a super-high-pressure mercury lamp 1 is passed through an optical path formed by an elliptical mirror 2, bending mirrors 4 to 6, lens 7 and a bending mirror 8 and illuminates a slit 9. The ultraviolet light is converted to a circular arc light by an opening in the slit 9, is then reflected by a mirror 10 and is divided into two portions by a half mirror 11. One of the light portions enters a light quantity monitor sensor 12 for keeping illuminance constant, and the other portion enters a shutter 13.
When the shutter 13 is open, the circular arc light is reflected by mirrors 14 and 15 and is applied to a mask 16. The light passing through the pattern of the mask 16 is reflected by a reflection type projection optical system comprising mirrors 17 to 19 and is then directed to a wafer 22.
Since the above apparatus employs an exposure system in which the mask and the wafer, which are maintained parallel, are scanned by the circular arc light at a constant speed, exposure must be kept constant by keeping the illuminance on an image plane constant during exposure. In addition, the illuminance on the image plane must be kept constant at each exposure in order to permit control of the exposure conditions at a scanning speed in the exposure process. The super-high-pressure mercury lamp must thus be maintained lighted in a stable state.
In order to obtain stable illuminance (luminance) after the super-high-pressure mercury lamp is lighted (started), the vapor pressure of mercury in the lamp must be stabilized from the viewpoint of the structural properties thereof. In the exposure apparatus, several tens of minutes after starting are required for stabilizing the lamp. In addition, although a high voltage must be applied to the lamp at the start, if the power source of the exposure apparatus is turned on, the super-high-pressure lamp can be lighted only in a state wherein the power supplied to the exposure apparatus is off because an error is produced in the exposure apparatus due to the discharge noise caused by the high voltage applied to the super-high-pressure mercury lamp. Namely, the super-high-pressure mercury lamp must be constantly lighted in a state wherein the exposure apparatus is operated, and it is necessary and indispensable that the illuminance is kept constant during a repeated exposure operation.
As described above, in the exposure apparatus, since the super-high-pressure mercury lamp is continuously constantly lighted, the optical parts nearer the super-high-pressure mercury lamp than the shutter are continuously exposed to the strong ultraviolet light. The surface of each of the mirrors and lenses serving as the optical parts is coated with a multilayer film for controlling the reflectance or transmittance. There are thus problems that the film is deteriorated due to irradiation with the ultraviolet light, and that the reflectance or transmittance is decreased due to the deposition of a gas floating in air above the film surface, which is caused by strong ultraviolet light.
In the exposure apparatus, a feedback loop for controlling the electric power supplied to the super-high-pressure mercury lamp 1 so as to keep the quantity of light entering the light quantity monitor sensor 12 constant during the repeated exposure operation, comprises a light quantity monitor sensor 12, a super-high-pressure mercury lamp 1 and a lighting device (driving device) (not shown) for the mercury lamp 1, whereby the illuminance on an image plane (mask surface) can be kept constant. Further, since the emission efficiency of the super-high-pressure mercury lamp 1 gradually deteriorates with lighting time, the deterioration is compensated for by increasing power supply. In this feedback loop, the power supply is thus continuously increased in view of a long-term operation. This lighting method is referred to as a xe2x80x9cconstant illuminance lighting methodxe2x80x9d.
If constant illuminance lighting is performed during both exposure and non-exposure, an electrode deteriorates, and the transmittance deteriorates due to the adhesion of foreign materials to the tube surface of the mercury lamp, which is caused by an increase in the internal temperature, thereby causing a problem that the performance of the super-high-pressure mercury lamp 1 deteriorates.
Accordingly, an object of the present invention is to provide an exposure apparatus that reduces deterioration in a light source and an optical system, and a method of producing a device such as a semiconductor memory, a liquid crystal panel, a magnetic head, a CCD or the like using the exposure apparatus.
In order to achieve the object, an exposure apparatus in a first preferred embodiment comprises a light source for supplying an exposure beam along an exposure path, a shutter for opening and closing the exposure beam path, and driving means for driving the light source to maintain the intensity of the exposure beam substantially constant when the exposure beam path is open, and to maintain current for driving the light source substantially constant when the path is closed.
In order to achieve the object, an exposure apparatus in a second preferred embodiment comprises a light source for supplying an exposure beam along an exposure beam path, a shutter for opening and closing the exposure beam path, and driving means for driving the light source to maintain the intensity of the exposure beam substantially constant when the path is open, and to maintain voltage for driving the light source substantially constant when the path is closed.
In order to achieve the object, an exposure apparatus in a third preferred embodiment comprises a light source for supplying an exposure beam along an exposure beam path, a shutter for opening and closing he exposure beam path, and driving means for driving the light source to maintain the intensity of the exposure beam substantially constant when the path is open, and to maintain electric power for driving the light source substantially constant when the path is closed.
In order to achieve the object, an exposure apparatus in a fourth preferred embodiment comprises a light source for supplying an exposure beam along an exposure beam path, an optical system for receiving the exposure beam, a first shutter provided on a downstream side of the optical system in the exposure beam path, for opening and closing the exposure beam path, and a second shutter provided on an upstream side of the optical system in the exposure beam path, for opening and closing the exposure beam path. The second shutter is opened before the first shutter is opened and closed after the first shutter is closed.
In order to achieve the object, a device producing method in one preferred embodiment comprises the steps of emitting an exposure beam from a light source along an exposure beam path, controlling incidence of the exposure beam on a substrate by opening and closing the exposure beam path, printing a device pattern on the substrate by exposing the substrate to the exposure beam when the path is open, and driving the light source to maintain intensity of the exposure beam substantially constant when the path is open, and to maintain the light source current for driving the light source substantially constant when the path is closed.
In order to achieve the object, a device producing method in another preferred embodiment comprises the steps of emitting an exposure beam from a light source along an exposure beam path, controlling incidence of the exposure beam on a substrate by opening and closing the exposure beam path, printing a device pattern on the substrate by exposing the substrate to the exposure beam when the path is open, driving the light source is driven to maintain intensity of the exposure beam substantially constant when the path is open, and to maintain voltage for driving the light source substantially constant when the path is closed.
In order to achieve the object, a device producing method in yet another preferred embodiment comprises the steps of emitting an exposure beam from a light source along an exposure beam path, controlling incidence of the exposure on a substrate by opening and closing the exposure beam path, printing a device pattern on the substrate by exposing the substrate to the exposure beam when the path is open, driving the light source to maintain intensity of the exposure beam substantially constant when the path is open, and to maintain electric power for driving the light source substantially constant when the path is closed.
In order to achieve the object, a device producing method in still another preferred embodiment comprises the steps of emitting an exposure beam from a light source along an exposure beam path, controlling incidence of the exposure beam on a substrate by opening and closing the exposure beam path, providing a first shutter for opening and closing the exposure beam path on the downstream side of the optical system and a second shutter for opening and closing the exposure beam path upstream of the optical system, the shutter on the upstream side being opened before the shutter on the downstream side is opened, and closed after the shutter on the downstream side is closed, and printing a device pattern on the substrate by exposing the substrate to the exposure beam when the exposure beam path is open.